The purpose of the study is to evaluate the thermal performance of the gas turbine unit represented by (K3) under actual weather conditions by applying the first and second laws of thermodynamics, the design production of the unit (283.6 MW) at standard conditions (1 bar) and temperature (15) Celsius, which included the analysis of the unit energy and available energy. To find out the weaknesses and losses in the system using the ChemCad simulation for a whole year and knowing the effects of external factors for the performance of the turbine unit (ambient temperature, compression ratio and relative humidity). Overall results showed that the maximum exergy efficiency was obtained in November; it was about 37% when Ta was 19.39°C. The maximum efficiency obtained at Ta equal to 19.39°C, which was around 37.67%. Higher ambient temperature increases specific fuel consumption. The results show that the specific fuel consumption (SFC) for the practical and program calculations increases with the increase in the temperature of the external environment and reached the maximum rate in the practical calculations in September (0.224) at 33.27°C. Thus it economically affects the price of power production. Moreover, the results showed that the combustion chamber occupied the first place for the destruction of available energy, and the results of energy efficiency and available energy were (39.20%) and (30.83%), respectively.